So the impact of a clockwise (or stopped) block came up and there's a case in the casebook that is confusing me.

specifically :

Scenario C4.17White Pivot stands still on their toe stops and initiates a block against Red Jammer. Red Jammer does not fall, but is brought to a stop. Red Jammer counter-blocks, but White Pivot continues to block while on their toe stops and Red Jammer is unable to get past.

Outcome: White Pivot is penalized.

Rationale: If Red Jammer loses position or has their momentum or trajectory severely affected by a block initiated in an unexpected way, the initiator should receive a penalty. In this example, if White Pivot had not maintained their stopped block but instead returned to counterclockwise skating, allowing Red Jammer to maintain part of their momentum, it would not have resulted in a penalty.

What's confusing is the rationale. The first sentence is saying to call a penalty because momentum or trajectory is severely affected. In this case the jammer got stopped.

But the second sentence says that if White Pivot had not maintained the stopped block they shouldn't get a penalty. It does say that some of the jammer momentum is maintained but the scenario says the jammer is stopped by the first block. So that is contradictory.

This came about from a discussion of clockwise (stopped) block impact when the jammer does not get knocked down or out of bounds.

You will often see skaters rotate in their tri-pods clockwise, bump the opposing jammer then continue in CCW direction. This case seems to suggest that these types of contact scenarios do not rise to the level a penalty. If the blocker were to continue driving into the jammer by taking another stride clockwise, then you should call a clockwise block penalty for impeding their progress. The last ruleset in the DoG section of the rules would explain this with more detail, making it clear that contact while stopped or clockwise, if it had no impact, would not be a penalty for impediment so long as the next action was stepping or skating in CCW direction.

Quote

What would we consider "momentum or trajectory severely affected"?

Taking an additional stride or step clockwise after the first (when the initiator doesn't fall, go down, or knocked severely off balance, where it is clear their progress is impeded). The example is saving space by providing all the possible combinations of this scenario at once.

I agree the jammer got stopped but I think the rule said "brought to a stop" to differentiate from red jammer's momentum being severely affected.

I used to call it "actively maintaining" a stopped block, where blocker had to step/skate counter clockwise or disengage to avoid the penalty

I would consider "momentum or trajectory severely affected" to mean the following

A fast moving jammer being stopped deadUpper body moved more than say 30 deg off centreA big direction changeBody positioning bent over with waving body parts trying to stay upright - you know when people nearly fall, but they don't

I can see where you're coming from on the casebook entry. There are quite a few negatives in that phrasing, "had not", "would not have". The rationale is that had the White Pivot started moving in the derby direction after the initial stopped block thereby allowing the Red Jammer to maintain some of their speed then all is well, no penalty.

Really what the casebook entry is stating is that bringing a fast moving skater to a complete stop via an illegal block is enough impact to trigger the "significantly alter speed or trajectory" metric.